Apparatus of transmitter and receiver for MIMO MC-CDMA system

ABSTRACT

The invention relates to an apparatus of transmitter and receiver for MIMO MC-CDMA systems. At the transmitter, modified orthogonal transmit diversity (MOTD) encoders are used for increasing space and time transmission diversity. A P-way combiner is used to connect the MOTD encoders and P multi-carrier modulators. Each modulator is connected to a set of antennas. At the receiver, each multi-carrier demodulator has an amplitude/phase compensator to compensate distortion at every sub-carrier. Similarly, a combiner is used to connect the demodulators and the MOTD decoders. Upon the invention, the space, time, and frequency diversity can be explored.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the technical field of wirelesscommunications and, more particularly, to a transmitter and receiverapparatus for Multiple Input/Multiple Output MultiCarrier-Code DivisionMultiple Access (MIMO MC-CDMA) systems.

2. Description of Related Art

A new generation cellular mobile communication system has to providewireless network applications with high-speed information transmission.Currently, it is known that MultiCarrier-Code Division Multiple Access(MC-CDMA) technique is one of the best solutions. CDMA is a coretechnique for the Third Generation Mobile Communication System, whichapplies Gold codes and OVSF (Orthogonal Variable Spreading Factor) codesto the system for allowing multiple users to concurrently transmit dataon a same band.

Multi-carrier modulation is the principle of transmitting data bydividing a high-rate data stream into several parallel low-rate datastreams onto individual carriers or subcarriers. By transmitting severalsymbols in parallel, the symbol duration is increased proportionately,which reduces the effects of ISI (Inter-Symbol Interference) caused bythe dispersive Rayleigh-fading environment. By transmitting symbols ontosubcarriers, frequency diversity is gained and thereby mitigating theeffects of narrow band interference and frequency selective fading. Dueto the advance of digital signal processing (DSP) and very large-scaleintegrated-circuit (VLSI), multi-carrier modulation is widely used inhigh-rate digital communications, such as digital broadcast, digitaltelevision and wireless local area network (WLAN). It is important inthe present and future wireless multimedia communications.

In communication theory, multiple input/multiple output (MIMO) refers toradio links with multiple antennas at the transmitter and the receiverside. Given multiple antennas, the spatial dimension can be exploited toimprove the performance of the wireless link.

In a typical MIMO MC-CDMA system, one multi-carrier modulator isconnected to one transmitting antenna. That is, the transmitter has thesame amount of multi-carrier modulators and transmitting antennas. TheInverse fast Fourier transform (IFFT) unit, which often occupies a largearea in an IC, is one of the most important, complicated and expensiveunits in a multi-carrier modulator. It means that multiple expensiveIFFT units are necessary for a typical MIMO MC-CDMA system.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an apparatus oftransmitter and receiver for multiple input/multiple outputmulticarrier-code division multiple access (MIMO MC-CDMA) systems,thereby effectively improving the system performance.

According to the present invention, an apparatus of transmitter for MIMOMC-CDMA systems is provided. The apparatus of transmitter includes amodified orthogonal transmit diversity (MOTD) encoder, a combiner, atleast one code spreader, at least one multi-carrier modulator and atleast one set of transmitting antennas. The information used forcommunication is divided into at least one data stream, which is thenfed into the MOTD encoder. The encoder consists of a symbol-mappingunit, a serial to parallel (S/P) converter, a splitter, and at least onecode spreader in which orthogonal codes are generally applied for.Thereby the at least one spread symbol stream is obtained and connectedto the combiner. At least one combined symbol stream is output from thecombiner. Each of it is spread by a code spreader in which PN codes,Gold codes, or orthogonal codes are generally applied for. The at leastone code spreader works as similar as the aforementioned code spreaderin the MOTD encoder. The code spreader in the MOTD encoder is named asthe first code spreader and the code spreader here is named as thesecond code spreader. Each output of the at least one second codespreader is connected to one multi-carrier modulator. In general, themodulator consists of an S/P converter, an IFFT unit, a parallel toserial (P/S) converter, and a cyclic prefix (CP) inserter. At least oneset of transmitting antennas is used for radiating the RF (RadioFrequency) signal stream, which is up converted from the output of themodulator. Each radiated signal stream by an antenna in one set isdelayed by small time duration.

According to the present invention, an apparatus of receiver for MIMOMC-CDMA systems is provided. The apparatus includes at least onereceiving antenna, at least one multi-carrier demodulator, at least onecode de-spreader, a combiner, and a MOTD decoder. Each received signalstream, which is down converted from the signal received by a receivingantenna, is connected to a multi-carrier demodulator. In general, thedemodulator consists of a CP remover, an S/P converter, an IFFT unit, aphase/amplitude compensator, and a P/S converter. The at least onedemodulated symbol stream is combined by a combiner. The output of thecombiner is connected to a code de-spreader and the output of thede-spreader is connected to a MOTD decoder. The decoder consists of atleast one code de-spreader in which orthogonal codes are generallyapplied for, a summer, a P/S converter and a symbol-demapping unit.Finally, the information is collected from the at least one data streamwhich is decoded from the decoder.

Other objects, advantages, and novel features of the invention willbecome more apparent from the following detailed description when takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an apparatus of transmitter forMIMO MC-CDMA systems according to an embodiment of the invention;

FIG. 2 is a schematic block diagram of the interior of anK-input/K*M-output MOTD encoder according to an embodiment of theinvention;

FIG. 3 is a schematic block diagram of the interior of asingle-input/M-output MOTD encoder according to an embodiment of theinvention;

FIG. 4 is a schematic diagram of the interior of a splitter according toan embodiment of the invention;

FIG. 5 is a schematic diagram of a K*M-input/P-output combiner accordingto an embodiment of the invention;

FIG. 6 a schematic block diagram of an apparatus of receiver for MIMOMC-CDMA system according to an embodiment of the invention;

FIG. 7 is a schematic diagram of a Q-input/single-output combineraccording to an embodiment of the invention;

FIG. 8 is a schematic block diagram of a single-input/K-output MOTDdecoder according to an embodiment of the invention;

FIG. 9 is a schematic block diagram of the interior of asingle-input/single-output MOTD decoder according to an embodiment ofthe invention; and

FIG. 10 is a schematic diagram of the interior of a summer according toan embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic block diagram of an apparatus of transmitter forMIMO MC-CDMA systems according to an embodiment of the invention. InFIG. 1, the apparatus of transmitter includes a K-input/K*M-outputmodified orthogonal transmit diversity (MOTD) encoder (labeled byK-MOTD-K*M encoder, which means the encoder is with K inputs and K*Moutputs) 11, a K*M-input/P-output combiner 12, P code spreaders 13, Pmulti-carrier modulators 14, P amplitude adjusters 15, a plurality oftime delays 16 and a plurality of antenna sets 17, where K≧1, M≧1, andP≧1. Each multi-carrier modulator 14 consists of a serial/parallel (S/P)converter 141, an Inverse Fast Fourier Transform (IFFT) 142, aparallel/serial (P/S) converter 143 and a cyclic prefix (CP) unit 144.

FIG. 2 is a schematic block diagram of the interior of a K-MOTD-K*Mencoder 21 according to an embodiment of the invention. In FIG. 2, theencoder 21 consists of K single-input/M-output MOTD encoders (MOTD-Mencoder). As shown in FIG. 2, D₁(t), . . . ,D_(k)(t) can be regarded asdata streams for different users or for different applications. Eachdata stream (such as D₁(t)) passes through a MOTD-M encoder 211 toincrease its transmit diversity and thus M orthogonal symbol streams(such as S_(1,1)(t), . . . S_(1,M)(t)) are obtained in parallel.

FIG. 3 is a schematic block diagram of the MOTD-M encoder according toan embodiment of the invention. As shown in FIG. 3, the MOTD-M encoderconsists of a symbol-mapping unit 31, an S/P converter 32, an M×Msplitter 33 and M first code spreaders 34 in which (quasi-) orthogonalcodes are generally applied for. In this embodiment, the constellationused in the symbol-mapping unit 31 can be any constellation, forexample, MPSK or MQAM. The S/P converter 32 converts an M serial inputsymbols into M parallel output symbols. The M×M splitter 33 makes Mcopies of each of the M output symbols and then dispatches them in arandom or a specific order (as described hereinafter). The output of theM first code spreader 34 are denoted by S₁(t), . . . S_(M)(t), whereO₁(t), . . . , O_(M)(t) are generally (quasi-) orthogonal.

FIG. 4 is a schematic diagram of the interior of an M×M splitter. Asshown in FIG. 4, the input symbols are denoted by A(1), . . . , A(M). Mcopies of them will be dispatched in M time slots with a random or aspecific order. FIG. 4 shows an example of a specific order., At T=0,the order from top to bottom is A(1), . . . , A(M). At T=D, where D is aunit of time delay, the order from top to bottom is A(M), A(1), . . . ,A(M-1). Accordingly, at T=(M-1)*D, the order from top to bottom is A(2),. . . , A(M), A(1).

FIG. 5 illustrates the K*M-input/P-output combiner 12 with P=1 (i.e., asingle output). The output is obtained by simply summing the K*M inputsymbols. With P>1 (i.e., multiple outputs), the K*M input symbols aremathematically operated and then P output symbols are generated. Forexample, the K*M input symbols are first divided into P groups. In eachgroup, all the symbols then sum to its output. Note that in FIG. 1, theP second code spreaders (C₁(t), . . . , C_(p)(t)) 13 can be the same ornot. The P amplitude adjusters 15 are used for adjusting thetransmission power of the antennas. FIG. 1 illustrates a case of equaltransmission power to every antenna 17. The time delays 16, which valuesare all smaller than the CP duration, lead to an frequency selectiveeffect in transmission. An interleaver may be inserted in front of theIFFT 142, thereby fairly treating all the symbol streams in thefrequency domain.

FIG. 6 is a schematic block diagram of an apparatus of receiver for MIMOMC-CDMA systems according to an embodiment of the invention. In FIG. 6,the apparatus of receiver includes Q antennas 61, Q multi-carrierdemodulators 62, a Q-input/single-output combiner 63, a code de-spreader64, a single-input/K-output MOTD decoder (MOTD-K decoder) 65, where Q≧1.Each multi-carrier demodulator 62 consists of a cyclic prefix (CP)remover 621, an S/P converter 622, a Fast Fourier Transform (FFT) 623, aphase/amplitude compensator 624 and a P/S converter 625.

FIG. 7 is a schematic diagram of an embodiment of aQ-input/single-output combiner 63. As shown in FIG. 7, the combiner 63sums the Q input symbols with equal gain to output, can be thereby namedas an Equal Gain Combiner (EGC). However, other combining mechanisms canalso be used. For example, the Q input symbols are squared before beingsummed to output. In the case, the combiner can thereby named as aMaximum Ratio Combiner (MRC).

The second code de-spreader (C(t)) 64 corresponding to one of the Psecond code spreader 13 in FIG. 1, for example, C(t)=C_(p)(t).

FIG. 8 is a schematic block diagram of a MOTD-K decoder, which consistsof K single-input/single-output MOTD decoders 81. As shown in FIG. 8,D₁(t), . . . ,D_(k)(t) can be regarded as different data streams fordifferent users or for different applications. Each stream (such asD₁(t)) is obtained by passing through a single-input/single-output MOTDdecoder (shown in the following).

FIG. 9 is a schematic block diagram of the interior of asingle-input/single-output MOTD decoder. As shown in FIG. 9, the decoderconsists of M first code de-spreader 91 in which (quasi-) orthogonalcodes are generally applied for, an M×M summer 92, a P/S converter 93,and a symbol-demapping unit 94. In this embodiment, all the decodingoperations are corresponding to the encoding operations in FIG. 3.

FIG. 10 is a schematic diagram of the interior of an M×M summer.Likewise, corresponding to the operations of the M×M splitter in FIG. 4,at T=0, the order from top to bottom is A(1), . . . , A(M). At T=D,where D is a unit of time delay, the order from top to bottom is A(M),A(1), . . . , A(M-1). Accordingly, at T=(M-1)*D, the order from top tobottom is A(2), . . . , A(M), A(1). If an interleaver is applied in amulti-carrier modulator, a de-interleaver (not shown) must be insertedafter the FFT 623.

The invention can improve the system performance, which has proved bythe simulation in a Rayleigh multi-path attenuation channel with Dopplereffect.

As cited, the invention adopts the structure of orthogonal transmitbranching (for example, multi- (single-) input/multi- (single-) outputmodified orthogonal transmit diversity (MOTD) decoders (encoders)). Theinvention also adopts the transceiver structure with multipleinput/multiple output (MIMO), thereby effectively improving the systemperformance.

Although the present invention has been explained in relation to itspreferred embodiment, it is to be understood that many other possiblemodifications and variations can be made without departing from thespirit and scope of the invention as hereinafter claimed.

1. An apparatus of transmitter for multiple input/multiple outputmulticarrier-code division multiple access (MIMO MC-CDMA) systems,comprising: a K-input/K*M-output MOTD encoder (where K≧1 and M≧1) withat least one data stream as its input and at least one symbol stream asits output; a combiner connected to the K-input/K*M-output MOTD encoder,which is with at least one combined symbol stream as its output; atleast one code spreader, each of which is connected to the combiner andspreads the combined symbol stream to generate a symbol stream as itsoutput; at least one multi-carrier modulator, each of which is connectedto the at least one code spreader; and at least one set of transmittingantennas used for radiating the at least one RF signal stream, each setof which is up converted from the output of the at least onemulti-carrier modulator.
 2. The apparatus of transmitter as claimed inclaim 1, wherein a transmitted signal stream radiated by an antenna iswith a delay.
 3. The apparatus of transmitter as claimed in claim 1,wherein a transmitted signal stream radiated by an antenna is with anamplitude adjuster in order to adjust its transmitting power.
 4. Theapparatus of transmitter as claimed in claim 1, wherein theK-input/K*M-output MOTD encoder comprises at least onesingle-input/M-output MOTD encoder, each of which is with: asymbol-mapping unit to which any multi-phase/multi-amplitudeconstellation is applied; a first serial/parallel (S/P) unit; asplitting unit which makes at least one copy of its input and dispatchesthe copy in a random or a specific order; and at least one first codespreader to which any (quasi-) orthogonal codes are applied.
 5. Thetransmitter apparatus as claimed in claim 4, wherein thesingle-input/M-output MOTD encoder (where M≧1) is with single input andat least one (M) output.
 6. The apparatus of transmitter as claimed inclaim 1, wherein each multi-carrier modulator is with a second S/P unit,an inverse Fourier transform (IFFT) unit, a first parallel/serial (P/S)unit and a cyclic prefix unit.
 7. The apparatus of transmitter asclaimed in claim 6, wherein each multi-carrier modulator has aninterleaver in front of the IFFT unit, to fairly treat each symbolstream in the frequency domain.
 8. An apparatus of receiver for multipleinput/multiple output multicarrier-code division multiple access (MIMOMC-CDMA) systems, comprising: at least one receiving antenna; at leastone multi-carrier demodulator; a combiner connected to the at least onedemodulator and generates a symbol stream through mathematicaloperations as its output; a code de-spreader corresponding to one of theat least one second code spreader in the transmitter; and a K-outputMOTD decoder (where K≧1) by which at least one data stream is decoded.9. The apparatus of receiver as claimed in claim 8, wherein eachmulti-carrier demodulator is with a cyclic prefix remover, a third S/Punit, an FFT unit and a second P/S unit.
 10. The receiver apparatus asclaimed in claim 8, wherein the K-output MOTD decoder comprises at leastone single-output MOTD decoder, each of which is with: at least onefirst code de-spreader to which any (quasi-) orthogonal codes areapplied; a summing unit; a third S/P unit; and a symbol-demapping unitto obtain a data stream as its output.
 11. The receiver apparatus asclaimed in claim 10, wherein the signal-output MOTD decoder is withsingle input and single output.
 12. The apparatus of receiver as claimedin claim 9, wherein each multi-carrier demodulator further has anamplitude/phase compensator to compensate some distortion.
 13. Theapparatus of receiver as claimed in claim 12, wherein each multi-carrierdemodulator further has a de-interleaver after the FFT unit.